Gaseous hydride compounds are widely used as precursors in chemical vapor deposition (CVD) processes for the manufacture of microelectronic components. The growth and quality of thin films formed from gaseous hydride precursors are highly dependent upon the purity of the precursor compounds and require extremely low concentrations of impurities in the precursors. Removal of impurities such as oxygen, carbon dioxide, and water to concentrations in the parts per billion (ppb) range is required for many ultra-high purity precursors. The cost-effective removal of impurities to these ppb levels is very difficult.
Ultra-high purity ammonia and related hydride gases, such as arsine and phosphine, are important precursors in CVD processes. For example, ammonia is used as a precursor to form silicon nitride as an inter-layer dielectric and passivation layer and to deposit metal nitrides for high performance transistors, light emitting diodes, lasers, and photodiodes. The electrical properties of semiconductor devices are greatly dependent on the level of impurities in the nitride layers, and the level of these impurities is directly related to the purity of the source ammonia used in the layer manufacturing process. Oxygen is a particularly detrimental impurity in ammonia because of the high reactivity of oxygen, and the maximum allowable concentration of oxygen in ultra-high purity ammonia is typically about 100 parts per billion by volume (ppbv).
Many hydride gas purification processes remove impurities by contacting the hydride gas with porous adsorbents and getter materials containing various metal oxides. These processes preferably utilize the adsorbent and getter materials in cyclic operation wherein spent adsorbent and getter materials are regenerated offline and returned to service. Regeneration typically is effected by heating in a reducing atmosphere containing hydrogen or other reducing agents.
As purity requirements for metal hydride precursors used in CVD processes become more stringent, there is a need for improved adsorbents, getters, and processes for removing impurities from precursor feed materials, particularly when the impurities include oxygen, carbon dioxide, and water. These improved processes should include longer operating time between regenerations as well as simpler and more effective regeneration methods. These needs are addressed by embodiments of the present invention described below and defined by the claims that follow.